Electrical insulator assemblies

ABSTRACT

An insulator assembly including an insulator with a lower part having a mounting bushing sealingly mounted thereon. The bushing being provided with a cylindrical body which is locatable over the groove, and can be shaped during manufacture to sealingly engage in the groove by a spinning technique.

This invention concerns electrical insulator assemblies, andparticularly but not exclusively such assemblies usable with powertransmission capacitors; and also a method of making such assemblies.

To date difficulties have often been encountered in satisfactorilymounting ceramic insulators on electrical equipment such as powertransmission capacitors. Particular difficulties can be encountered withcapacitors as these are generally filled with an inflammable liquid.This has particularly been the case due to the fact that precisedimensions cannot be obtained during the firing of ceramics andtherefore subsequent precision grinding has sometimes been required.Alternatively, metal soldering has been used but this is generally notsufficiently fire resistant to be wholly satisfactory.

The term “spinning technique” when used in the specification is to beunderstood as describing a technique where a rotatable wheel or otherprojection is spun relative to an item, with the item andwheel/projection being urged against each other to shape the item.

According to the present invention there is provided an insulatorassembly, the assembly comprising an insulator having a lower part forinsulatingly mounting on a member of fixture, and an upper partconnectable to an electrical source of the like, the lower part having amounting bushing thereon sealingly extendible around the insulator, withthe mounting bushing engaging in a circumferential groove in theinsulator.

The mounting bushing is preferably shaped in situ on the insulator toengage in the groove. The mounting bushing may be shaped by a spinningtechnique.

A seal may be provided between a part of the mounting bushing and theinsulator, and the seal may be made of rubber and desirably siliconerubber.

The insulator at the lower part is preferably non circular incross-section to prevent relative rotation of the bushing thereon, andmay be lobe shaped. A plurality of recesses may be provided to form thenon-circular cross-section, and the recesses may be locatedcircumferentially around the insulator, and may interconnect and be ofvariable depth.

The insulator is preferably made of a ceramic material and desirablyporcelain.

The mounting bushing preferably provides a mounting flange. The mountingflange may extend radially or may extend at an in use downwardsinclination. The mounting bushing may be made of metal and desirablystainless steel.

The mounting bushing may be in the form of part of the casing for acapacitor or other device.

The top part preferably comprises an electrically conducting connectingmember in communication with the interior of the insulator, and a capmember engageable over a part of the connecting member and engageablewith the insulator to mount the connecting member thereon.

Also according to the present invention there is provided an insulatorassembly, the assembly comprising an insulator having a lower part forinsulatingly mounting on a member of fixture, and an upper partconnectable to an electrical source or the like, the top part comprisingan electrically conducting connecting member in communication with theinterior of the insulator, and a cap member engageable over a part ofthe connecting member and substantially non-rotatably engageable withthe insulator to mount the connecting member thereon.

The cap member may be engageable with one or more formations on theinsulator to prevent relative rotation. The formations may comprise oneor more substantially longitudinal grooves in which one or morecorresponding indentations in the cap member are locatable. The capmember may be mounted on the insulator by a spinning technique to causethe cap member to engage with the insulator, and the cap member mayengage with a lip on the insulator.

The connecting member may extend through an opening in the cap member. Aflange may be provided on the connecting member engageable against theinsulator. The cap member may engage against the flange on theconnecting member.

A seal may be provided between the connecting member and the insulatorand the seal may be locatable between the connecting member and theinsulator.

The seal may be made of rubber and desirably silicone rubber.

The connecting member may be in the form of a bolt. The connectingmember and/or cap member may be made of brass.

The invention further provides an electrical insulator assembly for apower transmission capacitor, the assembly being according to any of thepreceding fourteen paragraphs.

The invention also provides a method of making an electrical insulatorassembly, the assembly being according to any of the preceding fifteenparagraphs.

The mounting bushing is preferably located on the insulator whilst thebushing has a substantially cylindrical body which locates over thegroove in the insulator, and the cylindrical body is subsequently urgedinto the groove. The urging is preferably performed by a spinningtechnique.

The bushing may be glued onto the insulator, and desirably by an epoxyresin glue, prior to the urging being carried out.

When the bushing is part of a casing, the spinning technique ispreferably carried out using a portable tool comprising one or morespinable members engageable against the bushing.

The cap member may be mounted on the insulator by a spinning technique,and the indentations in the cap member are preferably formed before thespinning technique.

Embodiments of the present invention will now be described by way ofexample only and with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic side view of a first electrical insulatorassembly according to the invention, with one end in part cross-section,the middle section omitted and the other end in full cross-section;

FIG. 2 is a diagrammatic side view of part of a component of theassembly of FIG. 1;

FIG. 3 is a cross-sectional view along the line A—A of FIG. 2;

FIG. 4 is a diagrammatic view of part of the one end of the assembly ofFIG. 1 with a component removed therefrom;

FIG. 5 is an end view of the assembly of FIG. 1;

FIG. 6 is a diagrammatic view similar to FIG. 4 but with part of theinsulator removed and part of the view in section;

FIG. 7 is a side view of a part of a second electrical insulatorassembly according to the invention;

FIG. 8 is a diagrammatic plan view of the part of FIG. 7;

FIG. 9 is a cross-sectional view along the line X—X of FIG. 8; and

FIG. 10 is a diagrammatic cross-sectional view through a furthercomponent according to the invention.

FIGS. 1 to 6 of the drawings show a first insulator assembly 10 suitablefor mounting on a power transmission capacitor which would typically befull of oil. The assembly 10 comprises a porcelain insulator 12 of agenerally conventional configuration including a plurality of radialprojections 14 and grooves 16.

At the lower (right hand as shown in FIG. 1) end of the insulator 12 acircumferential slot 18 is provided which upwardly ends in acircumferential projection 20. Located within the slot 18 is a stainlesssteel bushing 22. The bushing 22 comprises an annular flange 24 which isinclined towards the lower end of the insulator 12, and which includesan inner step 26 leading to a generally cylindrical body 28 whichlocates and generally follows the shape of the slot 18. A siliconerubber seal 30 locates in the inner step 26. The inclination of theflange 24 advantageously spreads any later loads from the insulator 12.

The bushing 22 is mounted on the insulator 12 as follows. Initially thebody 28 will have a substantially fully cylindrical shape, and as aresult of this the bushing 22 can be pushed onto the end of theinsulator 12 to abut the projection 20, with the seal 30 located inplace, and held thereon under load. Using a spinning technique and byrotating the insulator 12, the body 28 is shaped to locate in the slot18. During the spinning technique it is possible to ascertain when thebody 28 has been fully pressed into the slot 18 by the change inresistive forces encountered. This technique provides for a strong andefficient mechanical seal. The use of the spinning technique allowsslightly different shapes and sizes of slots 18 to be used as may beencountered with fired ceramic articles.

As can be seen from FIGS. 2 and 3 the lower end of the insulator 12 andhence bushing 22 when pressed thereon has a slightly non-circularcross-section, and is in fact lobe shaped. The lobe shape is provided bythree recesses 23 which interconnect circumferentially around the slot18. The recesses 23 are substantially identical and comprise amid-portion 25 of greatest extent which reduces gradually each way toend portions 27 of minimum extent, with end portions 27 of each recess23 being interconnected.

This non-circular cross-section means that in practice the insulator 12cannot be rotated within the bushing 22 pressed thereon, and when thebushing 22 is welded to or is part of a capacitor casing, no part of thebushing assembly 10 will rotate during the attachment or detachment ofparts to the top of the bushing. Whilst the lobe shape is non-circular,it has a constant diameter and thus is quite suitable for use in anaccurate spinning technique, with for instance a pair of diametricallyopposed spaces spinning wheels.

At the upper end of the assembly 10 a brass connecting bolt 32 isprovided. The bolt 32 has a hexagonal cross-section head 34 with acoaxial larger circular flange 36. The bolt 32 is held on the insulator12 by a brass cap 38. The cap 38 has a closed end with a hexagonalopening 40 through which the head 34 extends. Three equispacedlongitudinal slots 42 are provided on the upper end of the insulator 12,and corresponding indentations 44 on the inside of the cap 38 engage inthe slots 42. The indentations 44 are pre-formed before location of thecap 38 on the insulator 12. An annular silicone rubber seal 46 isprovided between the end of the insulator 12 and the bolt flange 36.

The upper end is formed by holding the cap 38 on the insulator 12 underload, and turning the bottom edge 39 inwardly using the spinningtechnique so as to engage with a lip 41 provided on the insulator 12 ashort distance from the upper end thereof. The indentations 44 may beurged to engage in the slots 42.

There is thus described a strong seal with the slots and correspondingindentations preventing relative rotation between the components. Theinvention therefore provides an insulator assembly with a number ofadvantageous features. Strong fire proof seals are provided at both endof the assembly, with both arrangements preventing relative rotationbetween the respective components. Whilst strong seals are provided, themanufacturing technique is readily repeatable and thus consistent andinexpensive. The techniques also allow variations in the dimensions ofthe fired ceramic to be incorporated.

FIGS. 7 to 9 show an embodiment of the invention in the form of a lid100 for a capacitor casing. The lid 100 comprises two openings 102 eachfor receiving an insulator similar to that described above. Each opening102 has a formation 104 provided therearound which is generally similarto the bushing described above. The formation 104 again comprises acylindrical body 106 which can be shaped by spinning to engage in a slotaround an insulator. A portable spinning tool would be provided to shapethe cylindrical body 106. The cylindrical body 106 extends to aninclined flange 108 again with an inner step 110 to locate a seal (notshown) thereon. The lid 100 has a raised central area 112 with a centralvent and filling hole 114.

In some instances and for instance with a casing lid which has openingson inclined surfaces, it may not be possible to mount a ceramicinsulator on an integral bushing formation. In this instance a separatebushing formation 116 may be provided as illustrated in FIG. 10. Thisbushing 116 is similar to the arrangement shown on the lid 100 above,again with a cylindrical body 118 and an inclined flange 120. In use ofthe bushing 116, the flange 120 would be welded onto the lid in anappropriate position. The bushing 116 may be welded into positionfollowing mounting on a ceramic insulator.

Various other modifications may be made without departing from the scopeof the invention. For example, the insulator may be a different shape ormay have a different form. In particular the lower end may have adifferent shape and in some instances a circular shape may beacceptable. A different connection may be provided at the upper end. Thebolt may have a different shaped head such as square.

Whilst endeavouring in the foregoing specification to draw attention tothose features of the invention believed to be of particular importanceit should be understood that the Applicant claims protection in respectof any patentable feature or combination of features hereinbeforereferred to and/or shown in the drawings whether or not particularemphasis has been placed thereon.

What is claimed is:
 1. An insulator assembly, the assembly comprising aninsulator having a lower part for insulatingly mounting on a member of afixture, and an upper part connectable to an electrical source, thelower part having a mounting bushing thereon sealingly extending aroundthe insulator, with the mounting busing engaging in a circumferentialgroove in the insulator, characterized in that the mounting bushingprovides a mounting flange at an upper end of the mounting bushing. 2.An insulator assembly according to claim 1, characterized in that themounting bushing is shaped in situ on the insulator to engage in thegroove.
 3. An insulator assembly according to claim 2, characterized inthat the mounting bushing is shaped by a spinning techinque.
 4. Aninsulator assembly according to claim 1, characterized in that a seal isprovide between a part of the mounting bushing and the insulator.
 5. Aninsulator assembly according to claim 4, characterized in that the sealis made of rubber.
 6. An insulator assembly according to claim 5,characterized in that the seal is made of silicone rubber.
 7. Aninsulator assembly according to claim 1, characterized in that thegroove has a base that is non circular in cross-section to preventrelative rotation of the bushing thereon.
 8. An insulator assemblyaccording to claim 7, characterized in that the base of the groove islobe shaped in cross section.
 9. An insulator assembly according toclaim 7, characterized in that a plurality of recesses are provided toform the non-circular cross section.
 10. An insulator assembly accordingto claim 9, characterized in that the recesses are locatedcircumferentially around the insulator.
 11. An insulator assemblyaccording to claim 9, characterized in that the recesses interconnect.12. An insulator assembly according to claim 9, characterized in thatthe recesses are of variable depth.
 13. An insulator assembly accordingto claim 1, characterized in that the insulator is made of ceramicmaterial.
 14. An insulator assembly according to claim 13, characterizedin that the insulator is made of porcelain.
 15. An insulator assemblyaccording to claim 1, characterized in that the mounting flange extendsradially.
 16. An insulator assembly according to claim 1, characterizedin that the mounting flange extends at a downwards inclination.
 17. Aninsulator assembly according to claim 1, characterized in that themounting bushing is made of metal.
 18. An insulator assembly accordingto claim 1, characterized in that the mounting bushing is made ofstainless steel.
 19. An insulator assembly according to claim 1,characterized in that the mounting bushing is part of the casing for acapacitor or other device.
 20. An insulator assembly according to claim1, characterized in that the upper part comprises an electricallyconducting connecting member in communication with the interior of theinsulator, and a cap member engageable over a part of the connectingmember and engageable with the insulator to mount the connecting memberthereon.
 21. An insulator, the assembly comprising an insulator having alower part for insulatingly mounting on a member of fixture, and anupper part connectable to an electrical source, the upper partcomprising an electrically conducting connecting member in communicationwith the interior of the insulator, and a cap member engageable over apart of the connecting member and substantially non-rotatably engageablewith the insulator to mount the connecting member thereon, characterizedin that the cap member and the insulator have complementary formationsthat are mutally engageable positively to prevent relative rotation. 22.An insulator assembly according to claim 21, characterized in that theformations comprise one or more substantially longitudinal grooves inwhich one or more corresponding indentations in the cap member arelocatable.
 23. An insulator assembly according to claim 21,characterized in that the cap member in mounted on the insulator by aspinning technique to cause the cap member to engage with the insulator.24. An insulator assembly according to claim 21, characterized in thatthe cap member engages with a lip on the insulator.
 25. An insulatorassembly according to claim 21, characterized in that the connectingmember extends through an opening in the cap member.
 26. An insulatorassembly according to claim 21, characterized in that a flange inprovided on the connecting member engageable against the insulator. 27.An insulator assembly according to claim 26, characterized in that thecap member engages against the flange on the connecting member.
 28. Aninsulator assembly according to claim 21, characterized in that a sealis provided between the connecting member and the insulator.
 29. Aninsulator assembly according to claim 28, characterized in that the sealis locatable between the connecting member and the insulator.
 30. Aninsulator assembly according to claim 28, characterized in that the sealis made of rubber.
 31. An insulator assembly according to claim 30,characterized in that the seal is made of silicon rubber.
 32. Aninsulator assembly according to claim 21, characterized in that theconnecting member is a bolt.
 33. An insulator assembly according toclaim 21, characterized in that the connecting member or cap member ismade of brass.
 34. A method of making an electrical insulator assemblycomprising an insulator having a lower part for insulatingly mounting ona member of a fixture, and an upper part connectable to an electricalsource, the lower part having a mounting bushing thereon sealinglyextending around the insulator, with the mounting bushing engaging in acircumferential groove in the insulator, characterized in that themounting bushing has a substantially cylindreical body and has amounting flange at an end of the mounting bushing, said methodcomprising locating the mounting bushing on the insulator with thecylindrical body over the groove in the insulator and the mountingflange at an upper end of the mounting bushing, and subsequently urgingthe cylindrical body into the groove.
 35. A method according to claim34, characterized in that the urging is performed by a spinningtechnique.
 36. A method according to claim 35, characterized in thatwhen the bushing is part of a casing, the spinning technique is carriedout using a portable tool comprising one or more spinable membersengageable against the building.
 37. A method according to claim 34,characterized in that the bushing is glued onto the insulator prior tothe urging being carried out.
 38. A method according to claim 37,characterized in that the bushing is glued onto the insulator by anepoxy resin glue.
 39. A method according to claim 34, characterized inthat the cap member is mounted on the insulator by a spinning techinque.40. A method according to claim 39, characterized in that the indentionsin the cap member are formed before the spinning techinque.
 41. A methodaccording to claim 34, comprising shaping the mounting bushing in situon the insulator to engage in the groove.
 42. An article of manufacturecomprising a power transmission capacitor and an electrical insulatorassembly, the electrical insulator assembly comprising an insulatorhaving a lower part for insulatingly mounting on a member of a fixture,and an upper part connectable to an electrical source, the lower parthaving a mounting bushing thereon sealingly extending around theinsulator, with the mounting bushing engaging in a circumferentialgroove in the insulator, characterized in that the mounting bushingprovides a mounting flange at an upper end of the mounting bushing.